private void button2_Click(object sender, EventArgs e) 
        { 
 if ((textBox3.Text == null ) ¦ ¦ (textBox2.Text == null)  ¦ ¦ (textBox1.Text == null)) 
      { 
                          
    string str = "<script language='JavaScript'>history.go(-1);</script>";
    HttpContext.Current.Response.Write(str);

       }

------解决方案--------------------
把这段 
if (rr == DialogResult.OK)  
               {  
                   //////这里要怎么写？  
               }  
zhijie改成直接return就行了。